Getter for induction flashing



March 28, 1950 '2. J. ATLEE El AL GETTER FOR INDUCTION FLASHING FiledJan. 19, 1949 "IPiL cl?! INVENTORS Zea J/lf/ee Dwmrofe W. Dun/1 /MM W ifo ncy5 Patented Mar. 28 1950 GETTER FOR INDUCTION FLASHING Zed J. Atlee,Des Plaines, and Dunmore W. Dunk,

Lincolnwood, 111., assignors to Dunlee Corporation, Chicago, 111., acorporation of Illinois Application January 19, 1949, Serial No. 71,732

8 Claims. 1

The present invention relates to thermionic tubes, such as X-raygenerators, rectifier tubes and the like and more particularly togettering means incorporated therein.

An important object of the present invention is to provide a new andimproved arrangement for gettering means within thermionic tubes.

A further object of the invention is to provide an X-ray generator, withan element containing gettering material which is so mounted that, whenflashed, a more efficient disposition of the gettering material isobtained than in the case of similar devices as previously manufactured.

Another object of the invention is to provide a new and improvedmounting arrangement for an element containing gettering material withina tube of the class described whereby, upon flashing of the element, thegettering material is substantially confined within a predetermined endportion of the tube envelope.

A still further object of the invention is to provide a new and improvedmounting arrangement in X-ray generators and the like devices for theelement containing the gettering material whereby the element may beflashed more readily by inductive heating than in the case of tubes asheretofore manufactured and without unduly heating adjacent parts of thetube.

A further important object of the invention is to provide a simple andinexpensive mounting arrangement within X-ray generators and likedevices for the element. containing the gettering material whereby, uponflashing of the element, the disposition of the gettering material willbe restricted to electrically unstressed portions of the tube envelope.

A still further object of the invention is to provide an X-ray generatorwith a combined glass-to-metal seal shield and support for an elementcontaining gettering material.

For a consideration of what is believed novel and inventive, attentionis directed to the following description in which the foregoing andnumerous other important objects and advantages of the invention willbecome apparent, and which description, taken together with theaccompanying drawing, discloses a preferred embodiment of the invention.

Referring to the drawing, Fig. 1 is a partial, sectional view takensubstantially longitudinally through an X-ray generator provided withgettering means in accordance with the present in vention; r

Fig. 2 is an enlarged fragmentary sectional view illustrating one of thedetails of the present relatively inemcient because of the highteminvention; and

Fig. 3 is a plan view illustrating the getter rin incorporated in thepresent invention.

Referring now to the drawings, in Fig. 1 is shown a portion of athermionic tube which, in this instance, is an X-ray generator, having acathode unit I0, and an anode unit H, the two electrode units beingenclosed within a glass envelope i2. In accordance with present uniformpractice in the industry, the anode electrode III is shown mounted uponthe end of a reentrant cylindrical portion [3 of the envelope by meansof a glass-to-metal seal indicated at It.

In order to protect the seal Hi from the detrimental efifects ofimpingement of stray electrons thereupon, a cylindrical metal skirt i5is preferably mounted upon the anode and which skirt extends in spacedelation around the cylindrical portion I3 and the seal [4. The end ofthe skirt l5 nearest the active ends of the electrodes fits snuglyaround the base of the anode unit It and is suitably secured theretosuch as by the set screws [6.

The structure as thus far described is in accordance with present commonpractice in X-ray generatormanufacture. It is, furthermore, commonpractice to provide a gettering means in a high vacuum tube forrendering innoxious the traces of gas remaining in the tube after theusual exhausting procedure, or as a final step thereof after the tubehas been sealed off. It is the purpose of the present invention,however, to provide a more efiicient arrangement of the gettering meansthan has been employed heretofore.

We are aware of the fact that it has been proposed heretofore to arrangegetter elements inside of a glass-to-metal seal shield associated withone of the electrode units, and specific reference is made to thestructures shown in Patents 2,260,927, Atlee, and 2,445,257, Atlee. Themounting arrangements for the getter elements as shown in these patentsare inherently relatively expensive and, moreover, they cannot beflashed by inductive heating without causing undue heating of remainingmetal parts and particularly the metal seal members. Accordingly it wasnecessary to bring out leads for the getter elements and which wereflashed by passing a current flow therethrough from a source of energyconnected to the lead terminals. Furthermore, because of the particulararrangement of the getter elements as shown, the gettering material,after flashing of the element, is deposited upon the metal surfaces ofthe seal shield and other parts so that the material is renderedperature to which these parts are heated during normal operation of thetubes.

In the prior Patent 2,242,160, Atlee, is shown a getter elementsupported by insulators upon a bracket and which is, in turn, supportedupon the end of the seal shield, the getter element being positioned inthe end pocket of the envelope whereby, following flashing of theelement, the gettering material is deposited upon the inner surface ofthe glass envelope. While a more efiicient deposition of the getteringmaterial is obtained in this case than in the case of the prior artpatents mentioned in the paragraph above, the supporting arrangement forthe getter element is relatively complicated and expensive. It will benoted that special guard means are required for preventing passage ofgettering material into the main portion of the envelope to the vicinityof the active ends of the electrodes. While such a mounting for thegetter element may be employed in the case of tubes having relativelylarge envelopes, the space requirements are such that it is impractical,if not impossible, to use such an arrangement in tubes of smalldimensions. This is true also in the case of getter arrangements shownin the first mentioned patents.

In accordance with the present invention, we mount a getter element inthe form of a ring directly upon one of the electrode structures in sucha manner so that it may readily be heated inductively by means of highfrequency energy without causing undue heating of the remaining parts ofthe tube. Moreover, the getter ring is so mounted that, upon flashing,the gettering material is deposited upon the inner surface of the endpocket of the envelope for the most efficient functioning thereof.Furthermore, the getter ring is so mounted upon the electrode structurethat the structure, itself, forms a barrier, or guard, confining thegettering material to the region of the end pocket and precludingpassage of the gettering material toward and deposition thereof uponelectrically stressed portions of the envelope. It is not necessary tobring out any leads to external terminals for the getter element nor isit necessary to provide any special bracket or other supporting meanstherefor. Furthermore, the mounting arrangement of the present inventionis extremely compact so that its space requirements are practically nil;and, since no extra parts are required for supporting the getterelement, substantial savings in cost of manufacture are effected.

Referring again to the drawing, we provide a getter element in the formof a split ring shown at l! and which, in turn, is mounted within anannular groove is provided on the inner wall of the skirt l5 adjacentthe free end thereof. The getter element ll preferably consists of alength of tubula wire filled with a suitable gettering material such asbarium, magnesium and, preferably, a mixture of such metals. Ihe wire isof a length slightly less than the inner circumference of the groove l8and is initially rolled to a diameter somewhat greater than the outsidediameter of the skirt !5 as indicated in Fig. 3. For assembly of thegetter element, the free ends of the wire are pressed together to aposition indicated by dotted lines in Fig. 3 and, following insertion ofthe ring into the end of the skirt, the wire will expand due to itsinherent resiliency and fit snugly within the groove 58. One side of thegetter wire is ground away so as to produce a reduced section 2! and thering is preferably so assembled within the skirt I5 that the reducedside of the ring faces toward the bottom of the groove [8.

In conditioning the X-ray tube for operation, it is necessary to removeall of the gas present within the envelope as well as the occluded gascontained in the electrodes and in the material of the envelope itself.The occluded gases are removed by baking or otherwise heat treating theentire device at a temperature slightly less than the softening point ofthe glass while keeping the exhaust means in operation. After all of thegas, including the occluded gases and oth-- er impurities, have thusbeen removed from the envelope, the exhaust connection may be sealed offand, as a final step, the getter element is flashed in order to form endproducts of the gettering material and any trace of gas or otherimpurities remaining in the envelope are rendered innocuous thereby.

With the getter element arranged as described, it may readily be flashedby inductive heating by passing high frequency electric energy throughan externally arranged coil indicated at 22. Attention is directed tothe fact that, for flashing the getter ring ll, only the free end of theskirt 15 need be positioned Within the induction coil 22. Because of thefact that the metal skirt i5 is electrically conductive, it will beheated by the '2 electrical currents induced therein and which heat israpidly transmitted to the getter ring ll. Of course, some heat will begenerated within the getter ring by electrical induction. Because of thefact that the skirt l5 surrounds the seal M, the metal part thereof issubstantially shielded from inductive currents so that it is not heatedto an extent likely to cause softening of the glass joined thereto andimpairment of the seal.

Particular attention is directed to the fact that the free end of theskirt 15 faces and extends into the pocket 24 formed between thereentrant portion l3 and the adjacent outer wall portion 25 of theenvelope. This end of the skirt is particularly well suited forsupporting the getter element for the reason that the adjacent envelopewalls defining the pocket 2 5 are electrically unstressed and hence arerelatively cool throughout the operation of the tube. This isparticularly true in the event that the tube is of the oil immersiontype, such as an X-ray generator adapted to be mounted within anenclosing housing containing either oil or gaseous dielectric coolingmedium. Upon fiashing of the getter ring H, the gettering materialescaping through 5 the thin Wall section 2| of the tubular wire involatilized form condenses upon contact with the relatively coolsurfaces of the inner walls of the envelope defining the pocket 24 asindicated by the dotted area. In the manufacture of tubes in accordancewith the present invention, the deposition of the gettering material isstrictly confined within the area of the pocket M as indicated by arelatively sharp line of demarcation at the end of the depositsubstantially in the radial plane of the free end of the skirt l5 and asindicated by the edge of the deposit 26.

An important feature of the present invention resides in the fact thatthe flashing of the getter, and. the extent thereof, can be closelyobserved by watching the density of the deposit upon the inner walls ofthe pocket 24 during the flashing operation. Excessive heating of thetube parts can be easily avoided by noting carefully when the gettercommences to flash and discontinuing further heating after a deposit ofdesired density the tube and which are absorbed by the deposit ofgettering material so long as the tube walls on which the deposit isformed are maintained relatively cool. The portion of the tube definingthe pocket 24 is remote from both the filament and the anode target sothat it is one of the coolest parts of the tube.

While the invention has been described with reference to the getter ringmounted on the inner side ofa glass-to-metal shield skirt, it is to beunderstood that this shield skirt merely forms a convenient mounting ina tube of the class described. Insofar as the present invention isconcerned, the shield skirt, in effect, merely provides a barrierextending between the getter ring and the central portion of the tubewhereby the gettering material volatilized from the .ring upon flashingthereof is retained entirely within the end pocket 24 and permitsdeposition of the gettering material upon the envelope side wallsthereof. It is understood that the volatilized gettering materialescaping from the getter ring disperses in a straight line; and, forthis reason, it is necessary that the getter ring be arranged onlyslightly inwardly from the free end of the skirt l5. It is, of course,not essential that the ring be mounted within a groove I8 as shown; butthis is preferred merely for reasons of space factor, simplicity, easeof construction and also the ease with which it may be flashed withoutunduly heating remaining adjacent parts of the tube.

While the invention has been described with particular reference to acertain embodiment thereof, it is desired that it be understood thatvarious changes and modifications may be made without departing from thespirit and scope of the invention. It is desired, therefore, that it beexpressly understood that the illustrated embodiment is merely by way ofexemplification rather than by way of limitation.

What we claim as our invention is:

I. In an X-ray generator having a pair of spaced apart electrode unitsenclosed within a glass envelope, the invention comprising a metallic,cylindrical glass-to-metal seal shield mounted by one end on one of saidunits, the inner wall of said shield being provided with an annulargroove and an annular getter ring mounted within said groove andretained in position thereby.

2. In an X-ray generator having a pair of spaced apart electrode unitsenclosed within a glass envelope, the invention comprising a metallic,cylindrical, glass-to-metal seal shield mounted by one end on one ofsaid units, the space within said shield being in open communicationwith the remaining space within said envelope only by way of the freeend of said shield, the inner wall of said shield being provided with anannular groove adjacent the free end thereof and a split metallicannular getter ring mounted within said groove and retained in positionby the resiliency of said ring.

3. In an X-ray generator having a pair of spaced apart electrode unitsenclosed within a glass envelope, said envelope including a reentrantsleeve portion defining a pocket in one end of said envelope, one ofsaid units being mounted on the end of said sleeve, a glass-tometal sealbetween said one unit and said sleeve portion, the invention comprisinga cylindrical metal skirt annularly secured at one end to the baseportion of said one electrode unit, the free end of said skirt extendingaround said seal in spaced relation therewith, the inner wall of saidskirt being provided with an annular groove adjacent the free endthereof, an annular getter element comprising a metal sheath containinggettering material, said getter element being mounted within said grooveand retained therewithin by the resiliency thereof.

4. In an X-ray generator comprising a pair of spaced apart electrodeunits enclosed within a glass envelope, said envelope including areentrant sleeve portion defining a pocket in one end of said envelope,one of said units being mounted on the end of said sleeve, aglass-tometal seal between said one unit and said sleeve portion, theinvention comprising a cylindrical, metal skirt annularly secured at oneend to the base portion of said one electrode unit, the inner wall ofsaid skirt being provided with a recess, and a getter element comprisinga metal sheath containing a gettering material mounted within saidrecess.

5. In an X-ray generator having a pair of spaced apart electrodesenclosed within a glass envelope, a glass-to-metal seal mounting one ofsaid electrodes in one end of said envelope, the invention comprising acylindrical, metal, seal shield mounted by one end on said oneelectrode, an annular getter element secured to the inner surface ofsaid shield adjacent the free end thereof, said getter element beingarranged in contacting relation with the surface of said shieldsubstantially throughout the full length of said element.

6. In an X-ray generator having anode and cathode electrodes enclosedwithin a glass envelope, said envelope including a reentrant sleeveportion defining a pocket in one end of said en velope, one of saidelectrodes being mounted on the end of said sleeve, a seal between saidone electrode and said sleeve portion, the invention comprising acylindrical, metal skirt annularly secured at one end to the baseportion of said one electrode, the free end of said skirt extendingaround said seal in spaced relation therewith, an annular getter elementcomprising a sheath filled with gettering material mounted directly uponthe end portion of said skirt and concentrically therewith, the diameterof said skirt being greater than the diameter of said element wherebysaid skirt provides a barrier for precluding passage of getteringmaterial from the region of said pocket to the remainder of the spacewithin said envelope upon the flashing of said element, said getterelement being exposed in straight line relation with the inner walls ofsaid envelope defining said pocket whereby, upon flashing of saidelement, gettering material therefrom will deposit upon the inner wallsof said pocket.

7. In a thermionic tube having anode and cathode electrode unitsenclosed within a glass envelope, said envelope including a reentrantsleeve portion defining a pocket in one end of said envelope, one ofsaid units being mounted on one end of said sleeve, said one unitincluding a cylindrical, metal member having a diameter greater thansaid sleeve portion, the invention comprising a getter ring consistingof a metallic sheath filled with gettering material, said ring beingadapted to be flashed by inductive heating from a source of energyarranged externally of said tube, means mounting said ring upon saidmember in thermally and electrically conductive relation with respectthereto, said ring having a diameter substantially greater than thediameter of said sleeve portion but less than the diameter of saidmembeiysaid ring being mounted concentrically with said sleeve portionand said 1nemher, said ring being exposed in direct line relation to theinner surface of said envelope pocket, said member defining a barrierbetween said ring and the inner wall surfaces of said envelope beyondthe region of said pocket whereby, upon flashing of said ring byinductive heating, said gettering material is deposited upon the wallsof said envelope pocket, the barrier formed by said member precludingpassage of gettering material from said pocket to the remaining spacewithin said envelope.

8. In a thermionic tube having anode and cathode electrode structuresenclosed within a glass envelope, said envelope including a reentrantsleeve portion defining a pocket in one end of said envelope, one ofsaid structures being mounted on the end of said sleeve portion, anannular glass-to-metal seal between said one structure and said sleeveportion, the invention comprising an annular metal member adjacent saidseal forming a part of said one structure having an outside diametergreater than the diameter of said seal, an annular getter elementconsisting of a length of hollow wire filled with gettering material,said getter element being adapted to be flashed by inductive heatingthrough means of high frequency energy supplied from externally of saidtube, said getter element having a diameter less than that of saidmember and greater than that of said seal, means mounting said getterelement on said member closely adjacent thereto on the side thereoffacing said pocket, said element being exposed in straight line relationwith respect to the envelope surface defining said pocket, said memberdefining a barrier between all portions of said element and the spacewithin said envelope on the opposite side of said member with respect tosaid element whereby, upon flashing of said element, all getteringmaterial therefrom will be retained within said pocket.

ZED J. ATLEE.

DUNMORE W. DUNK.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,260,927 Atlee Oct. 28, 19412,275,864 Record Mar. 10, 1942 2,341,941 Mouromtsefi et al. Feb. 15,1944

